This disclosure relates to automobile steering systems, and, more particularly, to a steer-by-wire system and the optimization of vehicle performance through the consideration of overall vehicle response in relation to a slip angle curve.
Traditionally, steering systems and braking systems for motor vehicles have each relied on the independent actuation of groups of components within the motor vehicle. Each group actuated typically has a single function by which control of the motor vehicle is maintained. For example, with respect to steering systems, at least the front steerable wheels have been traditionally mechanically linked together and are synchronously steerable. In systems utilizing four-wheel steering, typically the front wheels are mechanically linked to each other and are synchronously steerable while the back wheels, although they are in electronic communication with the front wheels and provide an angle of steering relative to the front wheels, are likewise mechanically linked to each other and synchronously steerable. In the electronic braking systems currently utilized, electronics evoke a response from hydraulic systems that apply the braking action to the wheels of the motor vehicle. During normal braking with an electronic braking system, a system computer interprets an operator input (driver stepping on the brake pedal), and a signal is transmitted to mechanical actuators to apply the brakes. With regard to the typical vehicle configuration, the braking traditionally remains independent of the steering and the steering traditionally remains independent of the braking. When the motor vehicle experiences either function, the other remains the responsibility of the operator.
The steering and braking functions of the traditional motor vehicle are related through the wheels of the motor vehicle. A typical motor vehicle wheel has a force versus slip angle curve (shown below with reference to FIG. 1) associated therewith that characterizes the lateral force applied to the wheel as a function of the angle at which the wheel xe2x80x9cslipsxe2x80x9d on the surface over which it moves. Such movement of the wheel is defined by a positively sloped curve for low slip angles, a peak, and a negatively sloped curve for high slip angles. In traditional steering systems that steer a set of at least two wheels in unison, a motor vehicle is generally not operated beyond the peak force. When the motor vehicle is operated beyond the peak force, however, it experiences a limit-handling condition in which operator control of the motor vehicle is compromised.
Steer-by-wire systems capable of steering the steerable wheels of a motor vehicle independently of each other, although not having been used in this manner heretofore, open new possibilities in vehicular control, viz., the effective operation of the motor vehicle over the entire range of the force versus slip angle curve, and, in particular, the effective operation of the motor vehicle in the negative slope area of the curve beyond the peak. Such an operation allows for the use of the motor vehicle steering as a backup to the braking.
A system for steering a motor vehicle includes a steering input system, a controller in electronic communication with the steering input system, and a plurality of roadwheel systems. Each of the roadwheel systems is in electronic communication with the controller, and each roadwheel system includes a steering actuator and a steerable wheel rotatably and operably connected to the steering actuator. The steerable wheel is configured to be angled relative to a direction of travel of the motor vehicle.
The controller of the system includes at least one input port configured to receive inputs either from an operator of the motor vehicle or from the vehicle itself. It also includes provisions for normal steering control in electronic communication with the input port and failed brake steering control in electronic communication with the input port. The failed brake steering control has provisions for both first and second failed brake steering controllers, both of which are in electronic communication with the steering actuator of the system. The first failed brake steering controller is configured to allow for the braking of the motor vehicle followed by the steering of the motor vehicle, while the second failed brake steering controller is configured to allow for the steering of the motor vehicle followed by the braking of the motor vehicle. The controller manages the coordination between normal steering control and failed brake steering control, as well as coordination between the first failed brake steering controller and the second failed brake steering controller.
A method of stopping the motor vehicle during travel includes angling a pair of the steerable wheels thereof in opposing directions, either away from each other or toward each other. As the angle of the steerable wheels increases, an increasing portion of the lateral force on the wheels acts in the longitudinal direction of the vehicle, thus slowing the vehicle. The direction of the motor vehicle can also be controlled by angling the pair of steerable wheels in opposing directions for stopping and adjusting the angle of the pair of steerable wheels. Alternatively, the direction of the motor vehicle can also be controlled by angling one of the steerable wheels for stopping and steering the motor vehicle with the other of the steerable wheels. In a preferred embodiment, the steerable wheel being angled is on the outside of the turn and the steerable wheel on the inside of the turn is used to steer the motor vehicle. In addition, it is preferred to have the steerable wheels angled toward the center of the vehicle as opposed to being angled away from the center of the vehicle.
Because the automobile industry is driven by consumer interest, and because improved vehicle performance is a desirable factor relating to such an interest, the industry is drawn to developing technology that allows a motor vehicle operator to experience improved vehicle performance without requiring that the operator expend any effort in an attempt to change his method of driving. The technological advancements illustrated by the use of the above-described system enable improved vehicle performance as a result of the objective control of the motor vehicle maintained by the electronics of a by-wire system without requiring any change to the inputs from the driver.